The author of this code presumably had to support [EBCDIC](https://en.wikipedia.org/wiki/EBCDIC) at some point, where the numeric values of the letters are non-contiguous (gaps exist between `I`, `J` and `R`, `S`, as you may have guessed).

It is worth noting that the C and C++ standards only guarantee that the characters `0` to `9` have contiguous numeric values for precisely this reason, so neither of these methods is strictly standard-conforming.

Looks like it attempts to cover both EBCDIC and ASCII. Your alternative method doesn&#39;t work for EBCDIC (it has false positives, but no false negatives)

C and C++ _do_ require that `&#39;0&#39;-&#39;9&#39;` are contiguous.

Note that the standard library calls _do_ know whether they run on ASCII, EBCDIC or other systems, so they&#39;re more portable and possibly more efficient.

I was wondering if it&#39;s possible to change the statusbar **icons** colour (**not** the statusbar colour, `colorPrimaryDark`)
![enter image description here][1]
Let&#39;s say I want this statusbar with:  
`&lt;item name=&quot;colorPrimaryDark&quot;&gt;@android:color/white&lt;/item&gt;`  

and the icons in black, is it possible?

Thanks.

**EDIT:**
 

&gt; New in the M developer preview: windowLightStatusBar. Flipping this on
&gt; in your theme tells the system to use a dark foreground, useful for
&gt; lighter colored status bars. Note the M preview seems to have a bug
&gt; where notification icons remain white, while system status icons
&gt; correctly change to semitransparent black.

from: **Roman Nurik** Google+ [post][2]
[![enter image description here][3]][3]


  [1]: http://i.stack.imgur.com/rjSMG.png
  [2]: https://plus.google.com/+RomanNurik/posts/4WBSonAZxt1
  [3]: http://i.stack.imgur.com/9aosx.png

Android statusbar icons color

If I use a **pixel or em value** for border-radius, the edge radius is always a **circular arc** or a **pill shape** even if the value is greater than the largest side of the element.  

When I use **percentages**, the edge radius is elliptic and starts at the middle of each side of the element resulting in an **oval or ellipse shape** :

![pixel (px) border radius][1]![percent (%) border-radius][2]

Pixel value for border-radius :
&lt;!-- begin snippet: js hide: true --&gt;

&lt;!-- language: lang-css --&gt;

    div {
       background: teal;
       border-radius: 999px;
       width: 230px;
       height: 100px;
       padding: 40px 10px;
       box-sizing: border-box;
       font-family: courier;
       color: #fff;
     }

&lt;!-- language: lang-html --&gt;

    &lt;div&gt;border-radius:999px;&lt;/div&gt;

&lt;!-- end snippet --&gt;


Percent value for border-radius :

&lt;!-- begin snippet: js hide: true --&gt;

&lt;!-- language: lang-css --&gt;

    div {
      background: teal;
      border-radius: 50%;
      width: 230px;
      height: 100px;
      padding:40px 10px;
      box-sizing:border-box;
      font-family:courier;
      color:#fff;
    }

&lt;!-- language: lang-html --&gt;

    &lt;div&gt;border-radius:50%;&lt;/div&gt;

&lt;!-- end snippet --&gt;

Why doesn&#39;t border radius in percentages act the same way as border-radius set with pixel or em values?

  [1]: http://i.stack.imgur.com/ecMlo.png
  [2]: http://i.imgur.com/XGkAcJA.png

Border-radius in percentage (%) and pixels (px) or em

In a custom library I saw an implementation:

    inline int is_upper_alpha(char chValue)
    {
        if (((chValue &gt;= &#39;A&#39;) &amp;&amp; (chValue &lt;= &#39;I&#39;)) ||
            ((chValue &gt;= &#39;J&#39;) &amp;&amp; (chValue &lt;= &#39;R&#39;)) ||
            ((chValue &gt;= &#39;S&#39;) &amp;&amp; (chValue &lt;= &#39;Z&#39;)))
            return 1;
        return 0;
    }

Is that an [Easter egg][1] or what are the advantages vs standard C/C++ method?

    inline int is_upper_alpha(char chValue)
    {
        return ((chValue &gt;= &#39;A&#39;) &amp;&amp; (chValue &lt;= &#39;Z&#39;));
    }

  [1]: https://en.wikipedia.org/wiki/Easter_egg_%28media%29


Why is the alphabet split into multiple ranges in this C code?

In a custom library I saw an implementation:
<pre><code class="hljs language-arduino">inline int is_upper_alpha(char chValue)
{
 if (((chValue >= 'A') &#x26;&#x26; (chValue &#x3C;= 'I')) ||
 ((chValue >= 'J') &#x26;&#x26; (chValue &#x3C;= 'R')) ||
 ((chValue >= 'S') &#x26;&#x26; (chValue &#x3C;= 'Z')))
 return 1;
 return 0;
}
</code></pre>
Is that an <a href="https://en.wikipedia.org/wiki/Easter_egg_%28media%29" target="_blank" rel="noopener noreferrer">Easter egg</a> or what are the advantages vs standard C/C++ method?
<pre><code class="hljs language-arduino">inline int is_upper_alpha(char chValue)
{
 return ((chValue >= 'A') &#x26;&#x26; (chValue &#x3C;= 'Z'));
}
</code></pre>

In my code I have loop in which I construct and over determined linear system and try to solve it:

    #pragma omp parallel for
    for (int i = 0; i &lt; n[0]+1; i++) {
        for (int j = 0; j &lt; n[1]+1; j++) {
            for (int k = 0; k &lt; n[2]+1; k++) {
                arma::mat A(max_points, 2);
                arma::mat y(max_points, 1);
                // initialize A and y
    
                arma::vec solution = solve(A,y);
            }
        }
    }

Sometimes, quite randomly the program hangs or the results in the solution vector are NaN. And if I put do this:

    arma::vec solution;
    #pragma omp critical 
    {
        solution = solve(weights*A,weights*y);
    }

then these problem don&#39;t seem to happen anymore.

When it hangs, it does so because some threads are waiting at the OpenMP barrier:

    Thread 2 (Thread 0x7fe4325a5700 (LWP 39839)):
    #0  0x00007fe44d3c2084 in gomp_team_barrier_wait_end () from /usr/lib64/gcc-4.9.2/lib64/gcc/x86_64-redhat-linux-gnu/4.9.2/libgomp.so.1
    #1  0x00007fe44d3bf8c2 in gomp_thread_start () at ../.././libgomp/team.c:118
    #2  0x0000003f64607851 in start_thread () from /lib64/libpthread.so.0
    #3  0x0000003f642e890d in clone () from /lib64/libc.so.6

And the other threads are stuck inside Armadillo: 

    Thread 1 (Thread 0x7fe44afe2e60 (LWP 39800)):
    #0  0x0000003ee541f748 in dscal_ () from /usr/lib64/libblas.so.3
    #1  0x00007fe44c0d3666 in dlarfp_ () from /usr/lib64/atlas/liblapack.so.3
    #2  0x00007fe44c058736 in dgelq2_ () from /usr/lib64/atlas/liblapack.so.3
    #3  0x00007fe44c058ad9 in dgelqf_ () from /usr/lib64/atlas/liblapack.so.3
    #4  0x00007fe44c059a32 in dgels_ () from /usr/lib64/atlas/liblapack.so.3
    #5  0x00007fe44f09fb3d in bool arma::auxlib::solve_ud&lt;double, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt; &gt;(arma::Mat&lt;double&gt;&amp;, arma::Mat&lt;double&gt;&amp;, arma::Base&lt;double, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt; &gt; const&amp;) () at /usr/include/armadillo_bits/lapack_wrapper.hpp:677
    #6  0x00007fe44f0a0f87 in arma::Col&lt;double&gt;::Col&lt;arma::Glue&lt;arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt;, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt;, arma::glue_solve&gt; &gt;(arma::Base&lt;double, arma::Glue&lt;arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt;, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt;, arma::glue_solve&gt; &gt; const&amp;) ()
    at /usr/include/armadillo_bits/glue_solve_meat.hpp:39

As you can see from the stacktrace my version of Armadillo uses atlas. And according to this documentation atlas seems to be thread safe: ftp://lsec.cc.ac.cn/netlib/atlas/faq.html#tsafe

**Update 9/11/2015**

I finally got some time to run more tests, based on the suggestions of Vladimir F.

When I compile armadillo with ATLAS&#39;s BLAS, I&#39;m still able to reproduce then hangs and the NaNs. When it hangs, the only thing that changes in the stacktrace is the call to BLAS:

    #0  0x0000003fa8054718 in ATL_dscal_xp1yp0aXbX@plt () from /usr/lib64/atlas/libatlas.so.3
    #1  0x0000003fb05e7666 in dlarfp_ () from /usr/lib64/atlas/liblapack.so.3
    #2  0x0000003fb0576a61 in dgeqr2_ () from /usr/lib64/atlas/liblapack.so.3
    #3  0x0000003fb0576e06 in dgeqrf_ () from /usr/lib64/atlas/liblapack.so.3
    #4  0x0000003fb056d7d1 in dgels_ () from /usr/lib64/atlas/liblapack.so.3
    #5  0x00007ff8f3de4c34 in void arma::lapack::gels&lt;double&gt;(char*, int*, int*, int*, double*, int*, double*, int*, double*, int*, int*) () at /usr/include/armadillo_bits/lapack_wrapper.hpp:677
    #6  0x00007ff8f3de1787 in bool arma::auxlib::solve_od&lt;double, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt; &gt;(arma::Mat&lt;double&gt;&amp;, arma::Mat&lt;double&gt;&amp;, arma::Base&lt;double, arma::Glue&lt;arma::Mat&lt;double&gt;, arma::Mat&lt;double&gt;, arma::glue_times&gt; &gt; const&amp;) () at /usr/include/armadillo_bits/auxlib_meat.hpp:3434


Compiling without ATLAS, only with netlib BLAS and LAPACK, I was able to reproduce the NaNs but not the hangs.

In both cases, surrounding `solve()` with `#pragma` omp critical I have no problems at all

Is armadillo solve() thread safe?

I am wondering if there is way that `std::cout` automatically will insert some predefined value between printed sequences.

For example:

    std::cout &lt;&lt; 2 &lt;&lt; 3 &lt;&lt; 33 &lt;&lt; 45 &lt;&lt; std::endl;

outputs

    233345

and I would like it to output

    2 3 33 45

and I know, that it&#39;s easy to:

    std::cout &lt;&lt; 2 &lt;&lt; &quot; &quot; &lt;&lt; 3 &lt;&lt;  &quot; &quot; &lt;&lt; 33 &lt;&lt;  &quot; &quot; &lt;&lt; 45 &lt;&lt; std::endl;

But I&#39;am wondering if there is a way to automate this, such as:

    std::cout &lt;&lt; set_some_separator(&quot; &quot;) &lt;&lt; 2 &lt;&lt; 3 &lt;&lt; 33 &lt;&lt; 45 &lt;&lt; std::endl;

Anyone aware of something like this being possible?

C++ cout auto separator

For the Intel architectures, is there a way to instruct the GCC compiler to generate code that always forces branch prediction a particular way in my code?  Does the Intel hardware even support this?  What about other compilers or hardwares?

I would use this in C++ code where I know the case I wish to run fast and do not care about the slow down when the other branch needs to be taken even when it has recently taken that branch.

    for (;;) {
      if (normal) { // How to tell compiler to always branch predict true value?
        doSomethingNormal();
      } else {
        exceptionalCase();
      }
    }

-----------------

As a follow on question for Evdzhan Mustafa, can the hint just specify a hint for the first time the processor encounters the instruction, all subsequent branch prediction, functioning normally?

Is there a compiler hint for GCC to force branch prediction to always go a certain way?

I know `.o` are object files, `.a` are static libraries and `.so` are dynamic libraries? What is their physical significance? When can I use some and when not?

What is the difference between .o, .a, and .so files?

Is it possible to declare a variable `extern constexpr` and define it in another file?

I tried it but the compiler gives error: 

&gt; Declaration of `constexpr` variable &#39;`i`&#39; is not a definition

in .h:

    extern constexpr int i;

in .cpp:

    constexpr int i = 10; 


How to declare constexpr extern?

My code is:

    #include &lt;stdio.h&gt;
    #include &lt;string.h&gt;

    void main()
        {
	    char string[10];
	    int A = -73;
	    unsigned int B = 31337;

	    strcpy(string, &quot;sample&quot;);

	    // printing with different formats
	    printf(&quot;[A] Dec: %d, Hex: %x, Unsigned: %u\n&quot;, A,A,A);
	    printf(&quot;[B] Dec: %d, Hex: %x, Unsigned: %u\n&quot;, B,B,B);
	    printf(&quot;[field width on B] 3: &#39;%3u&#39;, 10: &#39;%10u&#39;, &#39;%08u&#39;\n&quot;, B,B,B);

	    // Example of unary address operator (dereferencing) and a %x
        // format string 
	    printf(&quot;variable A is at address: %08x\n&quot;, &amp;A);

I am using the terminal in linux mint to compile, and when I try to compile using gcc I get the following error message:

    basicStringFormatting.c: In function ‘main’:
    basicStringFormatting.c:18:2: warning: format ‘%x’ expects argument
    of type ‘unsigned int’, but argument 2 has type ‘int *’ [-Wformat=]
    printf(&quot;variable A is at address: %08x\n&quot;, &amp;A);

All I am trying to do is print the address in memory of the variable A.


How to printf a memory address in C

Refering to [js0n.c][1]

The code syntax is as below:

        static void *gostruct[] =
        {
        	[0 ... 255] = &amp;&amp;l_bad,
        	[&#39;\t&#39;] = &amp;&amp;l_loop, [&#39; &#39;] = &amp;&amp;l_loop, [&#39;\r&#39;] = &amp;&amp;l_loop, [&#39;\n&#39;] = &amp;&amp;l_loop,
        	[&#39;&quot;&#39;] = &amp;&amp;l_qup,
        	[&#39;:&#39;] = &amp;&amp;l_loop, [&#39;,&#39;] = &amp;&amp;l_loop,
        	[&#39;[&#39;] = &amp;&amp;l_up, [&#39;]&#39;] = &amp;&amp;l_down, // tracking [] and {} individually would allow fuller validation but is really messy
        	[&#39;{&#39;] = &amp;&amp;l_up, [&#39;}&#39;] = &amp;&amp;l_down,
        	[&#39;-&#39;] = &amp;&amp;l_bare, [48 ... 57] = &amp;&amp;l_bare, // 0-9
        	[65 ... 90] = &amp;&amp;l_bare, // A-Z
        	[97 ... 122] = &amp;&amp;l_bare // a-z
        };
    
    ........
    .......
    
    l_bad:
    	*vlen = cur - json; // where error&#39;d
        return 0;
    
    ........
    ........

Can anyone explain what is being done here? What does syntax `[0 ... 255]` and 
`&amp;&amp;l_bad` do here?

  [1]: https://github.com/quartzjer/js0n

What is this &quot;[0 ... 255] =&quot; syntax in C?

If `buf` is a `malloc()` allocated char buffer, does `free(buf)` set/reset `errno`?

Let&#39;s say I want to write the buffer to a file, and then free it, as I don&#39;t need it any more.

Let&#39;s say the error policy for the code is to return -1 on an error. 

Is this a proper way to write out the buffer and error check without leaking memory?

    fputs(buf, somefile);
    free(buf);
    if (errno) return -1;

Or do I need to consider free possibly setting errno, as in...

    fputs(buf, somefile);
    if (errno){ 
        free(buf);
        return -1;
    }
    free(buf);

or, horror of horrors, 

    do { 
      fputs(buf, somefile);
      int save_errno = errno;
      free(buf);
      errno = save_errno;
      if (errno) return -1;
    } while(0);  
    
where the use of a block allows for a local save_errno to exist in various places should this need to be reused.  

All of this would seem to depend on whether free() sets errno.  

The [linux man page for free()](http://linux.die.net/man/3/free) is also the man page for `malloc()`, etc.  It mentions `malloc()` setting errno, but not `free()`. 

The [GNU C Library manual page for freeing dynamic memory](http://www.gnu.org/software/libc/manual/html_node/Freeing-after-Malloc.html#Freeing-after-Malloc) does not mention whether free() sets errno. 

So I wrote a short program to force a write error so I could see if free() reset errno, and it does not.  I&#39;m wondering if I should rely upon this result and the fact that free() is so essential that &quot;of course it doesn&#39;t set errno.&quot;  

    # See if free() resets errno on a bad write
    #include &lt;errno.h&gt;
    #include &lt;stdio.h&gt;
    #include &lt;stdlib.h&gt;
    #include &lt;string.h&gt;
    
    int main(int argc, char **argv)
    {
      char * buf = malloc(256);
      snprintf(buf,256,&quot;%s\n&quot;, &quot;Hello, World!&quot;);
    
      FILE *badfile;
    
      badfile = fopen(&quot;/dev/null&quot;,&quot;r&quot;);
   
      fputs(buf, badfile);
      free(buf);
      printf(&quot;%d\n&quot;, errno);
      printf(&quot;%s\n&quot;, strerror(errno));
    }



Does free() set errno?

After reading [this answer][2] about undefined behavior and sequence points, I wrote a small program:

    #include &lt;stdio.h&gt;

    int main(void) {
      int i = 5;
      i = (i, ++i, 1) + 1;
      printf(&quot;%d\n&quot;, i);
      return 0;
    }

The output is `2`. Oh God, I didn&#39;t see the decrement coming! What is happening here?

Also, while compiling the above code, I got a warning saying:

&gt; px.c:5:8: warning: left-hand operand of comma expression has no effect&lt;br&gt;
&gt;
&gt;       [-Wunused-value]   i = (i, ++i, 1) + 1;
&gt;                             ^

Why? But probably it will be automatically answered by the answer of my first question.

  [1]: https://stackoverflow.com/questions/30605380/bash-usr-bin-hydra-pmi-proxy-no-such-file-or-directory
  [2]: https://stackoverflow.com/a/4176333/2411320


What does i = (i, ++i, 1) + 1; do?

I need to find out whether a character in a string is an emoji.

For example, I have this character:

    let string = &quot;&#128512;&quot;
    let character = Array(string)[0]

I need to find out if that character is an emoji.

Find out if Character in String is emoji?

I know there are other topics on this, but I can&#39;t seem to find out how to implement it.

I&#39;m trying to limit a UITextField to only five characters.

Preferably alphanumeric, `-`, `.`, and `_`.

I&#39;ve seen this code:

    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange,
                           replacementString string: String) -&gt; Bool
    {
        let maxLength = 4
        let currentString: NSString = textField.text
        let newString: NSString =
                 currentString.stringByReplacingCharactersInRange(range, withString: string)
        return newString.length &lt;= maxLength
    }

and

    func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -&gt; Bool {

        let length = count(textField.text.utf16) + count(string.utf16) - range.length
        return length &lt;= 10
    }

How can I actually implement it? Which &quot;textfield&quot; should I swap out for my custom named UITextField?





Content Type	Original Author	Original Content on Stackoverflow
Question	Vladimir Ch.	View Question on Stackoverflow
Solution 1 - C++	Wintermute	View Answer on Stackoverflow
Solution 2 - C++	MSalters	View Answer on Stackoverflow

Why is the alphabet split into multiple ranges in this C code?

C++ Problem Overview

C++ Solutions

Solution 1 - C++

Solution 2 - C++

Border-radius in percentage (%) and pixels (px) or em

Android statusbar icons color

Attributions